The present invention relates to a photocurable organopolysiloxane composition or, more particularly, to an organopolysiloxane composition capable of being cured by the irradiation with ultraviolet light into a rubber-like elastomer having excellent flexibility.
There have been made hitherto various attempts to obtain an organopolysiloxane polymer crosslinkable when irradiated with light, particularly, rich in ultraviolet by introducing certain photosensitive groups into silicones as well as to obtain a photocurable composition containing such a photosensitive organopolysiloxane. One of the problems in the hitherto known photocurable silicone polymers or compositions is that the photocuring of these silicones or compositions containing the same does not proceed with a sufficiently high velocity by the irradiation with light. Further, the thickness of the cured body prepared therewith is limited and difficulties are encountered when a thick-walled cured body is desired by the irradiation with light. On the other hand, the prior art photocurable organopolysiloxane or a composition containing the same is susceptible to the inhibition of curing by the atmospheric oxygen so that the photocuring in the surface layer is sometimes badly influenced. A further problem in the prior art photocurable organopolysiloxanes or the compositions is the poor flexibility of the cured products obtained therewith.